Mass spectrometers generally include an ion source, which provide gas phase ions, a mass analyzer, which disperses the ions according to their mass-to-charge ratio (m/z) by applying electromagnetic fields, and a detector, which quantifies the abundance of the ions. Conventional time-of-flight (TOF) mass spectrometers (MS) are based on the difference in velocity attained by ions of different m/z when they are accelerated in a vacuum by an electric field. For time-of-flight mass spectrometry, the common arrangement for the measurement of this velocity is to place a detector at the end of the flight path and determine the time required for the ion to reach the detector after acceleration. So, for a distance (d) between the acceleration region and the detector and a flight time (t) of between the time of acceleration and detection, the velocity (v) will be v=d/t. Since the distance is the same for all ions, their arrival times are different with the smaller m/z ions arriving first and the larger m/z ions later. The dispersion in flight times according to the m/z provides this technique with its name, “time-of-flight” mass spectrometry.
The devices and methods described herein use ion optics to disperse ions according to their mass to charge ratio, wherein over a limited range of mass to charge ratios, the ion optics and the manner in which they are switchable enable enhanced mass resolution compared to conventional time-of-flight or distance-of-flight mass spectrometers. Mass resolution is generally limited by the physical dimensions of the mass spectrometer. The achievement of higher resolution in time-of-flight mass spectrometry (TOFMS) requires longer flight paths, but is accompanied by the concomitant loss of spectral-generation rate, duty factor/cycle, and thus, sensitivity and precision. In addition, it is appreciated herein that the cost of instruments goes up dramatically with each increment of improved mass resolution. It has been discovered that the devices and methods described herein, also referred to as Zoom-TOF, a substantial increase in resolution, sensitivity, and precision may be realized with no significant increase in size or cost of the instrument. Furthermore, Zoom-TOF may be implemented on existing TOFMS instruments or provided as a feature in new instruments at low cost. Alternatively, a significantly smaller-package TOF instrument can be designed with Zoom-TOF capability that offers equivalent performance to more conventional-size instruments.